1. Field of the Invention
This invention relates to a method for producing a milling disk with embedded inserts made of a hard alloy, a ceramic material, or similar hard materials, which has a centered bore in a base body of the disk and wherein tips of the inserts project at a circumference of the base body of the disk, and relates to a milling disk, which can be produced in accordance with the method.
2. Description of Related Art
Known milling disks of this type require an elaborate, time-consuming and expensive manufacturing process. For example, the base body of the disk is stamped out from a steel plate of a required thickness and is then deburred. The bores for the inserts, preferably embodied as hard alloy pins or the like with an appropriate round or uniform cross section, are inserted into the base body of the disk thus produced.
The hard alloy pins are pressed into the bores of the base body of the disk and soldered to the base body. Finally, at least the bore of the base body of the disk is inductively hardened and the milling disk is galvanized.
The milling disks produced in this way are not only expensive to produce, but they also have considerable disadvantages in their use. Since often only the area of the bore is inductively hardened, the outside of the milling disk only has a reduced hardness. The stamped base body of the disk is also not definitely level, because of which the bore cannot extend evenly, such as cylindrically. This hampers the reception of the bearing shaft and the stress on the disk bore causing a correspondingly great, uneven wear in this area. Moreover, this can lead to the formation of burs or whiskers in the area of the edges of the bore, which extend beyond the level surface of the base body of the disk. In case of an insufficient distance between the milling disks and the spacer disks this can lead to a blockage of the milling tool shaft when it is operated.
It is one object of this invention to provide a method for producing a milling disk of the previously mentioned type but with milling disks having a level outer area, great hardness and solid seating of the inserts that can be produced in a cost-effective manner.
This object is attained in accordance with this invention with a pulverulent metal sintering material that is filled into a receptacle of a mold of a compacting tool, which is matched to outer contours of the base body of the disk. Prefabricated inserts are placed into the poured-in metal sintering material and are positioned in the compacting tool. Following the introduction of the metal sintering material and positioning of the inserts in the compacting tool, a green compact is pressed in, and the green compact removed from the compacting tool with the inserts pressed into it is sintered and, if required, is afterwards subjected to hardening and/or surface treatment.
The inserts are prefabricated in a known manner, wherein a geometric shape is determined by the manner of application and use. The interlocking and frictional connection of the inserts with the base body of the disk is important. Thus a material is used for the base body of the disk which greatly shrinks during sintering and in this way holds the inserts frictionally in place with a press fit. The compacted and sintered base body of the disk can be hardened and, if required, can be subjected to a surface treatment, for example galvanically, without problems. The production process is considerably simplified and uses known method steps and devices.
The introduction of the metal sintering material and the positioning of the inserts in them can take place in different ways during the filling process. For one, initially only approximately half the filling process is performed. The inserts are introduced into the mold of the compacting tool and are positioned therein, and the filling process is completed thereafter or the inserts are maintained positioned in a radially adjustable manner in the mold of the compacting tool. Following the filling process, the inserts are positioned in the filled-in metal sintering material by means of radial displacement. However, further variations of the filling and positioning process are possible before the compacting process is initiated and performed.
In one embodiment which is particularly advantageous, a molybdenum-alloy sintering material is used as the metal sintering material, and the green compact is sintered at approximately 1200 to 1300xc2x0 C. in a protective gas atmosphere for approximately 60 to 90 minutes. During the sintering process this material shrinks in the radial and axial direction by approximately 1.5 to 2%. Thus the sintered density is increased by approximately 03 to 0.5 g/cm3 in comparison with the density of the green compact. This is a function of the initial density and the sintering parameters. The achieved residual porosity is less than 5 volume-percent.
The support of the inserts in the base body of the disk can be improved with hard alloy pins used as inserts which have at least one section with a reduced cross section in the axial direction, or hard alloy pins can be used as inserts each with a cross section that continuously tapers toward the tip.
The sintered green compacts are subjected to hardening with the addition of carbon. The low residual porosity can be precisely controlled by case-hardening the edges, which permits a defined hardening depth. Surface hardnesses of 60 Rockwell C, or 710 VPN, are possible, and the hardening depth advantageously is up to 0.8 mm, and hardness is greater than 600 VPN.
Based on the low residual porosity of less than 5 volume-percent, it is possible to subject the sintered milling disks to a surface treatment without pretreatment, for example electrogalvanization.
The milling disks produced in accordance with this method are distinguished in that prefabricated hard alloy pins, which have an undercut in the axial direction and are embedded in a sintered base body of the disk, are fixed in place in the form of inserts by shrinking the base body of the disk during sintering. Soldering of the hard alloy pins with the base body of the disk is omitted, but yet an improved support of the hard alloy pins in the base body of the disk is achieved. The sintered milling disk with the fixed hard alloy pins can be case-hardened and subjected to a surface treatment. To ease the insertion of the bearing shaft into the bore of the base body of the disk, the edges of the bore in the base body of the disk have bezels.